A wireless earphone is an application of wireless technology to a hands-free earphone so that a user can avoid the annoying wires and can easily talk and listen to music in various ways. Since the advent of the wireless earphone, it has been a good tool for mobile business people to improve efficiency. However, existing wireless earphones are all come with built-in rechargeable batteries. When the battery is low, the entire earphone must be taken out and charged. Hence, this causes inconvenience to the user. The user cannot use the wireless earphone as desired, and cannot meet the increasing demand of the user.